The Martian-type CO 2 -N 2 plasma flow obtained in the plasma generator of the SR5 arcjet facility has been simulated using two complementary fluid descriptions. An inviscid multitemperature monofluid description has firstly been used to evaluate the importance of the different chemical and exchange processes between the flow species. Then, a one-temperature Navier-Stokes description has been used to evaluate the influence of viscous and rarefaction effects. In the nozzle throat region, heat addition from the arc firstly leads to the establishment of a translation-vibration disequilibrium. Near the end of the nozzle throat, temperature and pressure increases allow more efficient exchange processes and lower this disequilibrium. In the nozzle diverging region, chemical and vibrational processes are quickly frozen as the flow strongly expands. Furthermore, a translation-rotation disequilibrium also occurs near the nozzle exit. Navier-Stokes simulation results evidence a quick increase of the diverging section boundary layers, and therefore most of the diverging section is in a fully viscous interaction regime. Moreover, rarefaction effects are predicted to appear near the nozzle exit walls. The experimental measurements carried near the nozzle exit confirm the thermal disequilibrium regime of the flow, predicted by the simulation results. Nomenclature anode = nozzle anode arc = nozzle electrical arc cathode = nozzle cathode chamber = facility vacuum chamber Da = Damköler number gas = facility gas flow generator = conditions upstream of the nozzle throat h = flow enthalpy, MJ=kg i = chemical species index Kn = Knudsen number k B = Boltzmann constant, 1:38065 10 23 J=K L = characteristic length, m M = flow Mach number _ m = mass flow, kg=s _ Q = heat transfer rate, kJ=s p = flow pressure, Pa R-T = rotation-translation processes T = flow translational temperature, K T rot = species rotational temperature, K T vib = species vibrational temperature, K T w = nozzle wall temperature, K V-D = vibration-dissociation processes V-el = vibration-electron processes V-T = vibration-translation processes V-V = vibration-vibration processes v = flow velocity, m=s ZT; T vib = nonequilibrium coupling factor for dissociation Z 1 = Parker rotational collision number E = energy transfer rate, kW = arc energy transfer efficiency = flow density, kg=m 3 = collisional cross-section, m 2 F = flow characteristic time, s vib = vibrational relaxation characteristic time, s

At Laboratoire d'Aérothermique low pressure stationary arc jets are used to simulate the plasma flow around a space probe during a hypersonic entry into a planetary atmosphere. This paper focuses on the experimental investigation of the species present in the flow produced at the exit of the supersonic nozzle in CO 2 -N 2 plasma mixtures similar to the Mars atmosphere. The thermal nonequilibrium of the internal modes of some radicals is examined together with the electron density and temperature.

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